Linear video editing
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Linear video editing is the process of selecting, arranging and modifying the images and sound recorded on videotape whether captured by a video camera, generated from a computer graphics program or recorded in a studio. Until the advent of computer-based non-linear editing in the early 1990s "linear video editing" was simply called “video editing.”
Television was primarily a live medium until the introduction of videotape. The function of shot edits, were, in live television production, performed by switching from among two or more cameras. This was (and is) accomplished using a video switcher, an electronic device capable of handling two or more synchronized video inputs and combining them into a video output. A switcher can be used to perform cuts between video sources, or any number of longer transitions, such as wipes, fades and dissolves, with multiple sources.
Actual live television is still basically produced in the same manner as it was in the 1950s (although transformed by myriad technical advances). However, the only way of airing the same shows again (and again...) before videotape was introduced was by filming shows using a kinescope (essentially, a video monitor paired with a movie camera). However, kinescopes (the films of television shows) suffered from various sorts of picture degradation, from image distortion and apparent scan lines to artifacts in contrast and loss of detail. Also, kinescopes had to be processed and printed in a film laboratory, making them somewhat dicey for broadcasts delayed for different time zones.
So, the primary motivation for the development of videotape was as a short- or long-term archival medium. Only after a series of technical advances spanning decades did videotape editing finally become a viable production tool on a par with film editing.
The first widely-accepted videotape in the United States was 2 inches wide and travelled at 15 inches per second. To gain enough head-to-tape speed, four video recording and playback heads were spun on a head wheel across most of the 2-inch width of the tape. (Audio and synchronization tracks were recorded along the sides of the tape with stationary heads.) This system was known as Quad, for quadruplex recording. See 2 inch Quadruplex videotape.
The resulting video tracks were slightly less than a ninety-degree angle (considering the vector addition of high-speed spinning heads tracing across the 15 inches per second forward motion of the tape).
Originally videotape was edited by physically cutting and splicing the tape, in a manner similar to film editing. This was an arduous process and not widely performed. When it was used, the two pieces of tape to be joined were painted with a solution of extremely fine iron filings suspended in carbon tetrachloride. This exposed the magnetic tracks, so that they could be aligned in a splicer designed for this task. The tracks had to be cut during a vertical retrace, without disturbing the odd-field/even-field ordering. The cut also had to be at the same angle that the video tracks were laid down on the tape. Also, since the video and audio read heads were several inches apart, it was not possible to make a physical edit that would appear correct in both video and audio. The cut was made for video and a portion of audio then re-copied into the correct relationship (the same technique as for editing 16mm film with a combined magnetic audio track).
The disadvantages of physically editing tapes were many: edited tapes could not be reused (in an era when videotapes frequently were, because of their high unit cost); the process required great skill, and often resulted in edits that would roll (lose sync); and, each edit required several minutes to perform.
The television show Rowan & Martin's Laugh-In was the first and possibly only TV show to make extensive use of this method.
A system for editing Quad tape "by hand" was developed by the 1960s. It was really just a means of synchronizing the playback of two machines so that the signal of the new shot could be "punched in" with a reasonable chance at success. One problem with this and early computer-controlled systems was that the audio track was prone to suffer artifacts (i.e. a short buzzing sound) because the video of the newly-recorded shot would record into the side of the audio track. A commercial solution known as "Buzz Off" was used to minimize this effect.
For more than a decade, computer-controlled Quad editing systems were the standard post-production tool for television. Quad tape involved expensive hardware, time-consuming setup, relatively long rollback times for each edit and showed misalignment as disagreeable "banding" in the video. That said, it should be mentioned that Quad tape has a better bandwidth than any smaller-format analogue tape, and properly handled could produce a picture indistinguishable from that of a live camera.
When helical scan video recorders became the standard it was no longer possible to physically cut the tape. At this point video editing became a process of using two video tape machines, playing back the source tape (or raw footage ) from one machine and copying just the portions desired on to a second tape (the edit master ).
The bulk of linear editing is done simply, with two machines and a device to control them. Many video tape machines are capable of controlling a second machine, eliminating the need for an external editing control device.
This process is 'linear', rather than non-linear editing, as the nature of the tape-to-tape copying requires that all shots be laid out in the final edited order. Once a shot is on tape, nothing can be placed ahead of it without overwriting whatever is there already. If absolutely necessary material can be inserted by copying the edited content onto another tape, however as each copy introduced generation-produced image degradation this is not desirable.
One drawback of early video editing technique was that it was impractical to produce a rough cut for presentation to an executive producer. Since executive producers are never familiar enough with the material to be able to visualise the finished product from inspection of a decision list, they were deprived of the opportunity to voice their opinions at a time when those opinions could be easily acted upon. Thus, particularly in documentary television, video was resisted for quite a long time.
Video editing reached its full potential in the late 1970s when computer-controlled edit suite controllers were developed, which could orchestrate an edit based on an edit decision list (EDL), using timecode to synchronize multiple tape machines and auxiliary devices. The most popular and widely used computer edit systems came from Sony, Ampex and the venerable CMX. Systems such as these were expensive, (especially when considering auxiliary equipment like VTRs, video switchers and graphics generators) and were usually limited to high-end post-production facilities.
Jack Calaway of Calaway Engineering was the first to produce a lower-cost, PC-based, "CMX-style" linear editing system which greatly expanded the use of linear editing systems throughout the post-production industry. Following suit, other companies, including EMC and
Strassner Editing Systems, came out with equally useful competing editing products.
While computer based non-linear editing has been adopted throughout most of the commercial, film, industrial and consumer video industries, linear video tape editing is still commonplace in television station newsrooms, and medium-sized production facilities which haven’t made the capital investment in newer technologies. News departments often still use linear editing because they can start editing tape and feeds from the field as soon as received since no additional time is spend capturing material as is necessary in non-linear editing systems.
